This invention relates to a new process for the manufacture of acetals of alpha-halogenated aldehydes. more particularly, it relates to an improved process for the manufacture of chloroacetaldehyde dimethyl acetal.
A number of processes for the manufacture of chloroacetaldehyde acetals are known and have been disclosed in the prior art. For example, Ullman, Enzyklopadie der technischen Chemie, 4th edition 1975, vol. 9 page 375, describes the manufacture of chloroacetaldehyde acetals by chlorinating vinyl compounds in alcoholic medium. U.S. Pat. Nos. 2,803,668 and also 4,130,592 teach the chlorination of vinyl chloride which produces considerable amounts of 1,1,-2-trichloroethane as a byproduct. Because of its similar boiling point, it is difficult to separate the by-product from the desired chloroacetaldehyde dimethyl acetal. Moreover, a particular disadvantage of these methods relate to the highly toxic nature of the vinyl chloride starting material.
The reaction of vinyl acetate and a halogen in the presence of excess alcohol has been known for many years: see U.S. Pat. Nos. 2,330,570 and 2,411,826 and J. Am. Chem. Soc., vol. 61 (1939) pages 1705-1706 by E. M. Filachione. The acetals were isolated from the reaction mixture by customary methods, e.g., by the addition of water and by subsequent extraction of the acetal layer with a water-immiscible solvent such as ether, chloroform or benzene. The organic extract was washed with water and/or an aqueous alkaline solution, such as sodium bicarbonate solution, in order to remove acid or other water-soluble by-products, after which the organic solvent was then distilled off and the acetal purified by distillation. Because of relatively poor yields (approximately 46 to 53%) and also that large amounts of solvent have to be distilled, the process is inappropriate for the manufacture of chloroacetaldehyde dimethyl acetal on an industrial scale.
U.S. Pat. No. 4,440,959 issued Apr. 3, 1984 to Wacker-Chemie GmbH relates to an improved process for the manufacture of chloroacetaldehyde dimethyl acetal by reacting vinyl acetate and chlorine in a methanolic solution at a temperature of less than 20.degree. C. When the addition of chlorine is completed, low boiling constituents are partially or completely distilled off from the reaction mixture. The liquid residue is neutralized with solid oxides or carbonates of calcium and magnesium while maintaining a temperature of from 20.degree. to 60.degree. C. until the aqueous extract has a pH of greater than 5. When neutralization is completed, the reaction mixture forms two liquid phases and the upper organic layer containing the desired product is separated and fractionally distilled. The patent states that pure chloroacetaldehyde dimethyl acetal is obtained as the main fraction with yields of more than 90% calculated on the amount of vinyl acetate.
The process described in U.S. Pat. No. 4,440,959 is a batch-type operation, and none of the prior art applicant is aware of relating to the production of such compounds teaches or suggests the use of a continuous or semi-continuous process.
Particularly where large scale industrial operations are contemplated, there is a need for a safe and economical, continuous process for the manufacture of acetals of alpha-halogenated aldehydes. The acetals described herein are useful as intermediates in the production of other compounds which have commercial uses.